Drum-type washing machines generally have a body that makes up the outer frame of the washing machine, a tub within the body for receiving and holding wash material, and a rotating drum within the tub driven by a motor. During the wash process, laundry within the rotating drum is repeatedly raised and dropped as it mixes with wash water within the tub. The drum rotates at varying speeds during different stages of the wash process, such as lower speeds during the wash cycle, and higher speeds during the drying or dehydrating cycle.
As the drum, which is loaded with wash material, rotates and water is added and removed from the wash material during a wash operation, the total weight of the loaded drum may become imbalanced. An imbalanced load within the rotating drum can cause the machine to vibrate or shake as the mass within the drum rotates, which can result in loud operation or even machine damage. To account for this imbalance, some drum-type washing machines use counter-weights to offset the imbalanced wash load. One type of counter-weight system includes spheres that can run in a track around the periphery of the rotating drum. As the drum rotates, the counter-weighting balls move to the opposite side of the drum than the imbalanced wash load to help counteract the load imbalance within the drum.
Even when counter-weights are used to counteract imbalanced wash loads, problems with vibration and excess noise can occur at certain drum rotation frequencies during the washing operation. For example, at some spin speeds, spherical balls used as counterweights can remain in a state of transition as they lag behind the drum spin speed. As this lag occurs, the transitioning counterweights sometimes correct the imbalanced load, but can also add to the imbalanced load while in transition. This effect is particularly prevalent close to resonance frequencies of the combined rotating mass of the drum and the wash material. These and other issues can be addressed as described herein.